Personification of the Cthulhu Mythos deity Atlach-Nacha, as seen in the Haiyore! Nyaruko-san series. Does not appear in the TV anime, but does appear in the Flash animations (Haiyore! NyaruAni).
In accordance with the spider deity she represents, Atoko's character design incorporates spider-like elements, e.g. a spider web-patterned kimono.